"Scientific research, carried out over the past two years on behalf of Birmingham City and Stoke-on-Trent City councils, which jointly own the hoard, has revealed that the Anglo-Saxon goldsmiths had discovered an ingenious way of, metallurgically, dressing mutton up as a lamb. It appears that they deliberately used a weak acid solution – almost certainly ferric chloride – to remove silver and other non-gold impurities from the top few microns of the surfaces of gold artefacts, thus increasing the surfaces’ percentage gold content and therefore improving its appearance. This piece of Anglo-Saxon high tech deception turned the surfaces of relatively low karat, slightly greenish pale yellow gold/silver alloys into high karat, rich deep yellow, apparently high purity gold."
If I recall correctly, they found that more depletion guilded stuff associated with women than with men. Eleanor gave a talk about the hoard and her study of it at a meeting of the historical metallurgy society in May this year.